Method and device for regulating the flow rate of formation fluids produced by an oil well

ABSTRACT

The present invention relates to a method of regulating the flow rate of formation fluids produced from a determined zone of an underground well whose cased wall is provided with orifices through which said formation fluids can pass, said method consisting in applying a tubular structure along the casing in said zone, which tubular structure prevents the fluids from flowing directly while also preserving a flow path along which the fluids can flow via the annular space outside the tubular structure so as to generate head loss. The invention also relates to a device for implementing said method, which device is essentially constituted by a radially-expandable tubular structure that can be applied against the inside wall of the casing, the structure being provided with means for preserving the flow of the fluids via a path running along the casing and along the structure, in order to generate head loss.

The present invention relates to completion techniques used whenstarting production from a deposit of hydrocarbons, of gas, of water, orthe like, and it relates more particularly to means for regulating theproduction flow rate from certain zones of an oil well or the like.

Generally, formation fluids, i.e. hydrocarbons, water, and gas, areextracted from a deposit by means of a borehole consolidated bymechanical casing cemented to the wall of the borehole. In zones thatpass through underground reservoirs, the casing and the layer of cementare perforated to put the formation fluids in communication with theinside of the well.

A well usually passes through a plurality of production zones of variousthicknesses, and it therefore includes different perforation zones. Theformation fluids are conveyed to the surface by means of productiontubing. The production tubing is centered relative to the casing, and isheld by a packer, thereby making it possible to isolate the fluidproduction zone from the upper portion of the well.

Because of the diversity of the soils and of the quality of the rocksthrough which the well passes, it is common for the various perforationzones in the well to produce differently, be it in terms of flow rate orin terms of quality of the fluid produced. Certain zones can producemore than others and/or the ratio between the quantity of hydrocarbonsproduced and the quantity of water produced can vary from one zone toanother. The same well might thus include zones that produce 80% waterand 20% oil, the water and the oil flowing together at a flow rate of500 barrels per day (500 bbl=79.3 m³), whereas an adjacent zone mightproduce a higher quantity of hydrocarbons, e.g. 30% oil, but at a lowerflow rate.

Since the flow rate is a function of the pressure difference between theformation and the well, the proximity of a high flow rate zone tends toreduce said pressure difference and thus to minimize the quantityactually produced by a lower flow rate zone.

Unfortunately, high flow rate zones are often zones that mainly producelarge quantities of water, or more precisely of brine that is unsuitablefor any use and that must be separated from the hydrocarbons and thatmust be disposed of, e.g. by being re-injected into a neighboring well.Such unwanted production is particularly troublesome in that it limitsthe total output of hydrocarbons. It should also be emphasized that theproduction flow rates and qualities of the various zones also vary overthe life of the well.

Various techniques are known for plugging perforations, e.g. byinjecting a gel or a cement into the zones to be treated, or by placinga sealing liner inside the casing. Thus, tubular preforms have beenproposed, designed to be put in place while they are in the foldedstate, in which they are relatively compact radially, and then to beunfolded to obtain a cylindrical shape whose outside diameter is closeto the inside diameter of the casing. It is also known, in particularfrom Document WO 94/25655, that a tubular preform can be constituted bya braid of flexible strands embedded in a resin that can be set underthe effect of heat, for example. That type of preform accommodates veryhigh degrees of expansion, thereby making it possible to insert thepreform through the production tubing, and thereby minimizing the costsof working over and restarting production.

All those techniques suffer from the drawback of totally stopping anyproduction from the treated zone, which can adversely affect the totaloutput from the well.

An object of the present invention is thus to provide means forregulating the flow rate of the zones to be treated, but without therebyeliminating said flow rate. The invention achieves this object by makingprovision to apply a tubular structure along the cased wall of a well,in the perforation zone to be treated, which tubular structure preventsthe fluids from flowing directly while also preserving a flow path alongwhich the fluids can flow via the annular space outside the tubularstructure so as to generate head loss.

The invention also provides a device for reducing the flow rate offormation fluids produced from a determined zone of an underground well,which device is essentially constituted by a radially-expandable tubularstructure that can be applied against the inside wall of the casing, thestructure being provided with means for preserving the flow of thefluids via a path running along the casing and along the structure, inorder to generate head loss. In other words, the tubular structure ofthe invention does not serve to plug the perforations of the casing, butrather merely to slow down the flow of the formation fluids at thetreated perforations.

In a more particularly preferred variant of the invention, these flowmeans are constituted by grooves extending from the central portion ofthe outside face of the tubular structure to at least one of the ends ofthe tubular structure, which grooves preferably extend helically or inthe form of zigzag lines.

In a more particularly preferred embodiment, the tubular structure isderived from the tubular structure taught by above-mentioned Document WO94/25655, and it is thus formed of a tubular sleeve constituted by abraid of flexible strands embedded in a settable composite material,and, on its outside face, it has an elastomer skin provided with groovesforming a flow path extending from the central portion of the outsideface that serves to cover the perforation orifices to at least one ofthe ends of the sleeve.

Finally, the invention also provides a method for putting the device ofthe invention in place.

Other details and advantageous characteristics of the invention appearfrom the following description given with reference to the figures, inwhich:

FIG. 1 is a diagrammatic axial section view of an oil well passingthrough two perforation zones, one of which can be treated by the flowrate regulation method of the invention;

FIG. 2 is a diagrammatic view showing the well shown in FIG. 1, after aregulator sleeve of the invention has been put in place;

FIG. 3 is a diagrammatic view showing a regulator sleeve of theinvention;

FIG. 4 is a side view in greater detail of the regulator sleeve beforeit is expanded;

FIG. 5 shows examples of groove profiles; and

FIGS. 6 and 7 are diagrams showing how the regulator sleeve of theinvention is put in place.

FIG. 1 shows a typical oil well that can benefit from the method of theinvention. This well is formed by a borehole 1 which, in this example,extends along an essentially vertical axis, and whose wall has beencased by means of metal casing 2 fixed to the wall by means of a layerof cement. Starting from the surface, the well passes through a largenumber of types of geological formation that are isolated by the casing.

In the zones capable of producing hydrocarbons, the casing and thecement layer situated in the annular space between the casing and thewall of the borehole are perforated by means of explosive charges inorder to re-establish the communication between the formation and thewell, and in order to enable the fluids from the formations Z1 and Z2 toenter the well via the perforations 3 and 4.

The top portion of the well is isolated from the production zones bymeans of a packer 5 which maintains production tubing 6 centered in thecasing; which tubing is smaller than the casing and conveys the fluidsproduced by the formations Z1 and Z2 to the surface. By way of example,the casing has a mean diameter lying in the range 110 mm to 180 mm (4½inches to 7 inches) and the production tubing has a diameter Dttypically lying in the range 55 mm to 160 mm (2⅛ inches to 6¼ inches).

It is frequent for the production zones to have heterogeneous flowrates. For example, the production zone Z1 can produce a flow rate{right arrow over (F)}_(i) of 500 barrels per day (0.9 liters persecond) of a fluid made up of 80% water and of 20% oil, with as a“driving force” a pressure differential between the formation and theinside of the well of about 100 psi (6.9 MPa), while the production zoneZ2 produces a flow rate {right arrow over (f)}_(i) of about 400 barrelsper day (0.7 liters per second) of a fluid made up of 30% water and of70% oil for a pressure differential of the same order of magnitude.

In order to increase the flow rate of the zone Z2 that is richer inhydrocarbons, it is possible to close off the perforations of the zoneZ1. However, the operations performed to plug the perforations are noteasily reversible, so that it would probably be difficult to access thezone Z1 subsequently to enable the well to produce effectively until itis depleted.

The present invention proposes to increase the head loss in the zone Z1of lesser interest in order to increase the pressure differential in thezone Z2 that is richer in hydrocarbons, but while maintaining a certainlevel of production from the zone Z1.

This may be obtained, as shown in FIG. 2, by diverting the flow from theperforations of the zone Z1 so as to lengthen the path followed by theformation fluids, thereby generating head loss. In the example shown,the head loss is formed by placing a tubular sleeve 7 in the zone Z1 anddeploying it to apply it intimately against the wall of the well. Thetubular sleeve is designed so that “leakage” occurs via at least one ofits ends, with the fluids flowing between the inside wall of the casingand the tubular sleeve, so that, after treatment, the zones Z1 and Z2produce respective flow rates of {right arrow over (F)}_(a) and {rightarrow over (f)}_(a).

For example, the flow is obtained by providing removal grooves in theoutside face of the sleeve. When the sleeve is provided with an outsideface constituted by a skin of resilient material of the rubber type, thegrooves can be sculpted by means of tools that are commonly used tore-shape the treads of used tires.

Assuming that the formation fluid has a relative density of 0.81, and adynamic viscosity of 0.005 Pa.s, then it can be shown that four drains,each of which has a width of 4 mm, a depth of 3.5 mm, and a length of 1m, make it possible to generate a pressure drop of about 50 psi (0.35MPa) in said zone Z1, and that this pressure drop is proportional todrain length, and inversely-proportional to the number of the drains.

By reducing the production flow rate from the zone Z1 to about 100barrels per day, it is thus possible to increase the pressuredifferential in the zone Z2, e.g. to about 200 psi (1.4 MPa), whichmakes it possible to achieve a flow rate for that zone of about 600barrels per day, thus bringing the total output of oil produced by thewell to 440 barrels per day, i.e. increasing it by about 15%, but aboveall the volume of co-produced water (which needs to be separated fromthe oil at the surface) is halved, which reduces the cost of producingthe barrels of oil considerably.

In a more specially preferred variant of the invention described belowwith reference to FIGS. 3 and 4, the sleeve is provided with two seriesof grooves: drainage grooves 8 situated in the central portion of thesleeve that serves to cover the perforation zone, and removal grooves 9situated in at least one of the end zones.

The drainage grooves are of cross-section that is large enough to ensurethat the flow of the production fluids is substantially not slowed down.In addition, the grid layout formed by the grooves is preferably denseenough for the removal channels of the end zones to be well irrigated.

In the end zones, the grooves are typically smaller, e.g. shallower.FIG. 5 shows a few examples of groove profiles. In the simplest variant(FIG. 5A), the grooves are parallel to the longitudinal axis of thesleeve. However, this variant is not preferred if high head loss isdesired because it then requires sleeves that are very long andtherefore more costly.

The groove profiles shown in FIGS. 5B and 5D are other more speciallypreferred variants: helical variants (FIG. 5B), grooves forming zigzaglines (FIG. 5C), or crisscross grooves, e.g. of the crisscross helicalgroove type (FIG. 5D).

The shaped face is carried by a sleeve which, in its non radiallyexpanded form, must have a radial section that is smaller than thesection of the casing, and preferably even smaller than the section ofthe production tubing, thereby making it possible to perform thetreatment of the invention without prior removal of the productiontubing. That is why the sleeve is preferably a variant of the sleevetaught by Patent Application WO 94/25655, the contents of which isincorporated herein by reference. The sleeve is thus preferablyconstituted by a tubular structure provided with a jacket formed byinterlacing flat strands or tapes that are helically wound and embeddedin a thermo-settable resin, and confined between two resilient membranesmade of an elastomer material, the outer membrane forming the skin inwhich the drainage grooves of the invention are sculpted. For example,the strands may be formed of glass fibers, or preferably of carbonfibers. Preferably, the outside face of the outer skin is provided witha certain number of annular projections to facilitate good contact withthe casing.

FIGS. 6 and 7 show the operation of putting the sleeve of the inventionin place. Firstly, the sleeve, while not expanded radially, is insertedinto the well via the production tubing so as to be placed in thevicinity of the zone having the perforations 3 to be treated. For thispurpose, the sleeve is associated with a laying tool. The laying tool isessentially constituted by a die 10 having an inflatable element 11suspended from a cable 12 containing electricity feed means and pumpingmeans for inflating and deflating the die by means of the surroundingfluids. The die is provided with a series of resistor elements (notshown). The grooved outside skin 13 of the sleeve and its inside portion14 constituted by the braid embedded in the resin are shown, and thesleeve is fixed to the die by breakable link elements.

After positioning, the pump is started, and the die is graduallyinflated to anchor it against the wall of the casing, starting from thebottom upwards so as to expel any fluid present between the casing andthe sleeve. The radial expansion is thus achieved by deforming thebraided portion so that the sleeve is applied intimately against thecasing. Once the die and the sleeve have been fully deployed, anelectric current is applied to the resistor elements of the die to heatthe thermo-settable resin of the sleeve, thereby causing it topolymerize. Once the resin has been set in this way, the pump is used todeflate the die so that the die and the sleeve come apart after tractionon the cable to break the breakable link elements. The laying tool canthen be brought back up to the surface.

1. A method of regulating the flow rate of formation fluids producedfrom a determined zone of an underground well whose cased wall isprovided with orifices through which said formation fluids can pass,said method consisting in applying a tubular structure along the casingin said zone, which tubular structure prevents the fluids from flowingdirectly while also preserving a flow path along which the fluids canflow via the annular space outside the tubular structure so as togenerate head loss, wherein the tubular structure is deployed againstthe wall of the well such that formation fluids flow between the innerwall of the casing and the tubular structure.
 2. A method according toclaim 1, in which said path is helical.
 3. A device for regulating theflow rate of formation fluids produced from a determined zone of anunderground well whose wall is cased with casing provided withperforation orifices to allow said formation fluids to pass through it,said device being constituted by a radially-expandable tubular structurethat can be applied against the inside wall of the casing, the structurebeing provided with means for preserving the flow of the fluids via apath running along the casing and along the structure, in order togenerate head loss.
 4. A device according to claim 3, characterized inthat said flow means are constituted by removal grooves extending fromthe central portion of the outside face of the tubular structure to atleast one of the ends of the tubular structure.
 5. A device according toclaim 4, characterized in that said removal grooves are disposedhelically.
 6. A device according to claim 4, characterized in that saidremoval grooves are disposed in the form of zigzag lines.
 7. A deviceaccording to any one of claims 3 to 6, in which, in its central portionserving to cover the perforation zone, a tubular sleeve is provided withdraining grooves for collecting the incoming flow.
 8. A device accordingto any one of claims 3 to 6, in which the tubular sleeve is constitutedby a braid of flexible strands embedded in a settable compositematerial, and, on its outside face, it has an elastomer skin in whichthe removal and drainage grooves are provided.
 9. A method for puttingthe device according to claim 8 in place in a well equipped with casingand with production tubing, said method comprising: inserting a layingtool via the casing, which tool comprises an inflatable die providedwith heater elements and covered with the tubular sleeve, which die issuspended from a cable containing electricity feed means and pumpingmeans; inflating the die until the sleeve is applied against the insidewall of the casing; heating the die to polymerize the settable compositematerial; deflating the die while leaving the sleeve in place; andremoving the laying tool from the well.